Low-mass X-ray binary MAXI J1421-613 observed by MAXI GSC and Swift XRT
Abstract
Monitor of All sky X-ray Image (MAXI) discovered a new outburst of an X-ray transient source named MAXI J1421-613. Because of the detection of three X-ray bursts from the source, it was identified as a neutron star low-mass X-ray binary. The results of data analyses of the MAXI GSC (Gas Slit Camera) and the Swift XRT (X-Ray Telescope) follow-up observations suggest that the spectral hardness remained unchanged during the first two weeks of the outburst. All the XRT spectra in the 0.5-10 keV band can be well explained by thermal Comptonization of multi-color disk blackbody emission. The photon index of the Comptonized component is ≈ 2, which is typical of low-mass X-ray binaries in the low/hard state. Since X-ray bursts have a maximum peak luminosity, it is possible to estimate the (maximum) distance from its observed peak flux. The peak flux of the second X-ray burst, which was observed by the GSC, is about 5 photons cm-2 s-1. By assuming a blackbody spectrum of 2.5 keV, the maximum distance to the source is estimated as 7 kpc. The position of this source is contained by the large error regions of two bright X-ray sources detected with Orbiting Solar Observatory-7 (OSO-7) in the 1970s. Besides this, no past activities at the XRT position are reported in the literature. If MAXI J1421-613 is the same source as (one of) these, the outburst observed with MAXI may have occurred after a quiescence of 30-40 years.
- Publication:
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Publications of the Astronomical Society of Japan
- Pub Date:
- April 2015
- DOI:
- 10.1093/pasj/psv003
- arXiv:
- arXiv:1502.01077
- Bibcode:
- 2015PASJ...67...30S
- Keywords:
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- methods: data analysis;
- X-rays: bursts;
- X-rays: individual (MAXI J1421-613);
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 7 pages 5 figures